One mid-winter ward round, in an overflowing, under-pressure hospital, I was given a dressing-down by one of my patients. She was in her 80s and in pretty good nick, apart from the chest infection. She pointed at her breakfast tray – laden with Weet-Bix, toast, jam, stewed fruit, orange juice and tea. “It’s a disgrace,” she said. “At home I eat Bircher muesli and fresh blueberries for breakfast. Blueberries are full of antioxidants. You should look it up. You should hire a dietician. How do you expect us to get better if you feed us like this?” I wanted to ask her how long she imagined she’d be here, how much money she imagined was allocated to each patient’s meal and which political party she’d voted for. I’d back her long-term dietary plan, but toast and jam for a few days wasn’t going to kill her, nor hinder her recovery.

What you eat or avoid most of the time matters. A couple of serves of oily fish a week has modest positive effects on cardiovascular risk factors. Lifelong consumption of more vegetables than most people eat decreases the risk of dementia, cancer, heart disease and stroke. However, judging from headlines and my patients’ stories, the healthiest people in the healthiest countries are increasingly attributing magical properties to fairly ordinary food: properties both medicinal and toxic. Gwyneth Paltrow allegedly said that she’d kill herself before serving her children instant noodles. A friend of a friend claimed that crushed pumpkin seeds cured her exhaustion and her mother’s rheumatoid arthritis. Patients ask me if certain foods are the cause of their depression, anxiety, fatigue, their syncope, their multi-limb paralysis. Gluten, lactose, fructose, sugar, meat. Pity the chefs facing the now kaleidoscopic array of intolerants. Currently, the most common adverse effect of food is obesity. Serious food allergies exist – three sesame seeds hidden in a muesli bar almost killed one of my daughters – but they are relatively rare. We can test for coeliac disease (an immune-mediated inflammatory disease), and for lactose and fructose malabsorption. But dietary micro-manipulation, while satisfying or distracting and sometimes fascinating, can’t cure everything.

During a medical school lecture on the layout of the human gut, our professor of anatomy told us that the lumen of the oesophagus, stomach, intestines and rectum were not – technically – inside our bodies. “The alimentary canal,” he said, “is outside of you.” We were all, like, “Woah.” It was our first year and I was in a constant state of “woah”. I put his proposition into my sack of facts and eventually forgot it was there. It wasn’t until I found myself splayed on the floor of a Boeing 747 toilet, arms and chin pressed into the plastic seat like it was my mother, my head in the bowl for nine hours straight, that I remembered his claim. Who the hell cares? I thought. What’s your point? I thought. At that moment my alimentary canal did not feel as if it was outside of my body. My protesting, secreting, in-reverse-gear gut had become my entire being.

Turns out that almost every textbook of anatomy or physiology mentions (sometimes with an exclamation mark!) that the gut lumen is outside of the body. Not many go on to explain why this fact is not just a piece of nerd trivia. But consider this: chew something – say, a piece of steak – then swallow. Somehow in that outside–inside tunnel the meat will be churned, broken down and eventually absorbed. That is, there’s stuff in the lumen of our guts that can dissolve a cow. And that stuff, those enzymes and acids, have to be kept “outside” our insides or – given we’re basically hunks of walking Wagyu – we’d dissolve.

The borders of our gut are under heavy patrol. Tiny armies cling there and defend us, but if there’s war, there’ll be collateral damage. (And allergies are when our immune system attacks something it need not.) We do our best to avoid battle: pasteurisation, boiling, baking, hand hygiene, the five-second rule. The hospital kitchen’s main concern (apart from how to adequately feed a human on a few bucks a day) is how to keep food bacteria-free. We have an inside and an outside, but we are permeable. Our bodies are under constant assault: pathogens, malodours, sharp objects, bright light, thunderous noise. This permeability exposes us to risk but also allows us to procreate, to grow, to feel.

Food is a source of sustenance, pleasure and comfort. National identities rest upon it. Preparing it or sharing it can be an act of love, and the time we devote to it is commensurate with the rewards we receive. Food can cause harm if we’re allergic, if it’s full of pathogens or if we eat far too much. Soylent, a brand of home-delivered “complete nutrition” liquid championed by young male tech-types, is efficient, safe and very clean. You don’t have to prepare, taste or chew. Petrol for the engine, and you can fill ’er up in one minute flat. Low risk. Low pleasure.

The plane touched down and we were asked to stay seated. A quarantine officer – part of our country’s immune system – boarded to interview me before anyone could leave. I opened one eye and explained that, given my symptoms, I had most likely ingested staphylococcal toxin a few hours before take-off. Some chef had a festering finger-wound; the bugs jumped into the food and gleefully excreted their toxins (which are impervious to heat though it kills the actual bugs). I swallowed, the toxin wreaked havoc in my lumen, and my lumen responded with forceful expulsion per mouth. The quarantine officer listened to the neat summary of my travel history, symptomatology, physical findings and diagnosis, and allowed us to disembark (me in a wheelchair). I thought I’d never eat again. I’d be an all-food intolerant. They’d have to feed me Soylent through a nasogastric tube. Twenty-four hours later I was thinking, Turkish or Vietnamese?

Karen Hitchcock is a doctor and writer. She is the author of a collection of short fiction, Little White Slips, and the Quarterly Essay ‘Dear Life: On Caring for the Elderly’.

One mid-winter ward round, in an overflowing, under-pressure hospital, I was given a dressing-down by one of my patients. She was in her 80s and in pretty good nick, apart from the chest infection. She pointed at her breakfast tray – laden with Weet-Bix, toast, jam, stewed fruit, orange juice and tea. “It’s a disgrace,” she said. “At home I eat Bircher muesli and fresh blueberries for breakfast. Blueberries are full of antioxidants. You should look it up. You should hire a dietician. How do you expect us to get better if you feed us like this?” I wanted to ask her how long she imagined she’d be here, how much money she imagined was allocated to each patient’s meal and which political party she’d voted for. I’d back her long-term dietary plan, but toast and jam for a few days wasn’t going to kill her, nor hinder her recovery.